Ferritic stainless steel such as SUS430 is being broadly used for household electrical appliances, kitchenware, etc. Stainless steel has excellent corrosion resistance as its biggest feature. Therefore, it is also made into products in the form of a base metal without applying any surface treatment.
When shaping ferritic stainless steel, sometimes relief shapes called “ridging” are formed on its surface. If the steel surface suffers from ridging, the beautiful surface appearance will be ruined. Further, polishing for removing the ridging will become necessary. As means for improving the ridging resistance in the type of steel such as the SUS430 which becomes a dual phase of α+γ in the hot rolling temperature region, the following techniques are known. (For example, PLTs 1 to 4.)
PLT 1 discloses the technique of prescribing the amount of Al and the amount of N in the steel, bending the steel in the middle of hot rolling, and changing the crystal orientation by subsequent recrystallization. PLT 2 shows the technique of prescribing a compression rate at the time of hot final rolling.
PLT 3 discloses the technique of making the rolling reduction rate per pass 40% or more, giving a large strain, and splitting the ferrite bands. PLT 4 discloses the technique of adjusting the steel to an austenite phase rate which is calculated by the composition of ingredients and prescribing the heating temperature, the final rolling speed, the temperature, etc.
However, with the techniques which are disclosed in PLTs 1, 2, and 4, depending on the type of steel, the ridging resistance is sometimes not necessarily improved. Further, in the technique which is disclosed in PLT 3, sometimes galling defects are formed at the time of rolling. In this case, the productivity falls. In the above way, in steel becoming a dual phase of α+γ in the hot rolling temperature region, at the present, no technique has been established for improving the ridging resistance.
On the other hand, in recent years, it has been studied to add a fine amount of Sn to improve the corrosion resistance or high temperature strength of low Cr ferritic stainless steel. (For example, PLTs 5 to 7.) PLT 5 discloses ferritic stainless steel which has a Sn content of less than 0.060%. PLT 6 discloses martensitic stainless steel characterized by an Hv300 or more high hardness. PLT 7 discloses ferritic stainless steel in which Sn is added to improve the high temperature strength.